This invention relates generally to electrocardiographic localization and classification of cardiac arrhythmias. More particularly, the present invention relates to noninvasive analysis of TU wave obscured atrial activity.
An arrhythmia is any deviation from or disturbance of the normal heart rhythm. This is when the heart""s natural pacemaker develops an abnormal rate or rhythm (e.g. a tachycardia where the heart rate is faster than normal), the normal conduction pathway is interrupted, an abnormal or accessory conduction pathway controls the rhythm, or when another part of the heart takes over as an ectopic pacemaker. Arrhythmias may be benign, life threatening or even fatal depending on the type of arrhythmia. Several different types of arrhythmias can be distinguished, for example atrial tachycardia, atrioventricular (AV) node reentrant tachycardia, atrial fibrillation, atrial flutter, and ventricular tachycardia.
Although electrocardiographic arrhythmia evaluation is currently feasible by capturing spontaneous tachycardia episodes via ambulatory or emergency electrocardiogram (ECG) recording, analysis of the timing and presumed origin of atrial activation on the body surface is frequently hampered by the simultaneous occurrence of the higher voltage ventricular activation or recovery potentials. During both focal and incisional reentrant atrial tachycardia, the low-amplitude P wave (atrial activity) may be obscured by the preceding high-amplitude QRST segment (ventricular activity). Difficulties are encountered when visually assessing the P wave morphology of TU wave superimposed ectopic atrial beats that are critically related to atrial fibrillation triggered by a focal source, typically situated in one of the pulmonary veins. Similarly, localization of the atrial insertion site using the retrograde P wave morphology obtained during orthodromic AV reentrant tachycardia may be difficult due to partial or complete concealment by the TU wave.
The ability to completely isolate the P wave from a preceding cardiac cycle is particularly relevant with regard to recent reports describing the role of focal triggers in the initiation of atrial fibrillation (e.g. Haissaguerre, M. et al. (1998) Spontaneous initiation of atrial fibrillation by ectopic beats originating in the pulmonary veins, N. Engl. J. Med. 339:659-666). Localized adequately, these focal triggers are amenable to treatment and cure using radiofrequency catheter ablation. However, mapping of the premature beats that cause the initiation of atrial fibrillation using standard catheter techniques is cumbersome, lengthy, and unpredictable. Therefore, noninvasive electrocardiographic localization of these atrial premature beats before or during the invasive mapping procedure is highly preferable. However, since the P wave of these atrial premature beats is usually obscured by the preceding TU wave, application of a QRST subtraction algorithm to isolate and preserve the detailed P wave morphology is of critical importance to enable ECG-based trigger localization. However, to date no such algorithms exist that are capable of isolating and preserving the detailed P wave morphology.
So far, most people use QRST subtraction algorithms to detect P waves, fibrillation waves, or flutter waves by either a frequency analysis (e.g. U.S. Pat. No. 6,064,906), morphological filters (e.g. Sedaaghi, M. H. (1998), ECG wave detection using morphological filters, Appl. Sign. Process. 5:182-194), suppression and cross correlation techniques (e.g. U.S. Pat. No. 5,840,038), or an impulse correlated adaptive filter (e.g. Zhu Y. S. and Thakor N. V. P (1987), P-wave detection by an adaptive QRST cancellation technique, In: Computers in Cardiology; Eds. Ripley K. L., IEEE Comput. Soc. Press, Washington, D.C., pp. 249:252). A previously reported method on QRST algorithms employs additional measures to correct for rate-related differences in QRST duration (e.g. Slocum J. et al. (1992), Diagnosis of atrial fibrillation from surface electrocardiograms based on computer-detected atrial activity, J. Electrocardiol. 25:1-8). In addition, in previous reports and methods, the design of the QRST templates was done on the same data set that was subsequently subjected to QRST removal. In that case, the presence of AV dissociation was considered imperative to ensure that atrial activity would be preserved in the remaining signal after QRST subtraction.
Although, most of the before mentioned methods work well for P wave or fibrillation wave detection, they do not provide the ability to retain important spatial and temporal details regarding the specific morphology of the atrial activity. There is therefore a strong need for an improved clinical tool to achieve adequate isolation of TU wave superimposed atrial activity so that noninvasive electrocardiographic screening, localization and analysis of atrial arrhythmias can be carried out more effectively before or during an invasive electrophysiologic intervention.
In light of the above, it is the primary objective of the present invention to provide an apparatus and method for electrocardiographically localizing and classifying atrial arrhythmias. More specifically, it is the objective of the present invention to provide a noninvasive apparatus and method for analysis of TU wave obscured atrial activity.
It is another objective of the present invention to provide an automatic QRST subtraction algorithm based on using an adaptive QRST template constructed from averaged QRST complexes combined with ECG recordings to enable discrete isolation of TU wave obscured ectopic atrial activity on the surface ECG while retaining the intricate spatial and temporal details in P wave morphology.
It is yet another objective of the present invention to obtain an optimal morphology subtraction performance in the TU wave range by correcting specifically for differences in both the QRST duration and voltage of the T wave.
It is still another objective of the present invention to provide a QRST template design based on a separate data set obtained during sinus rhythm and/or atrial pacing to ensure that atrial and ventricular activity are clearly separated.
It is still another objective of the present invention to provide for an optimal visualization of the P wave morphology in both supraventricular arrhythmias (i.e. atrial tachycardia and orthodromic AV reentrant tachycardia) and focal atrial ectopy where atrial activity coincides with ventricular recovery of the preceding cardiac cycle.
It is another objective of the present invention to isolate P waves from the superimposed TU wave during AV associated rhythms other than atrial ectopy (e.g. flutter waves in atrial flutter).
It is another objective of the present invention to isolate fibrillation waves during atrial fibrillation and to provide a clinical tool to achieve noninvasive localization of the triggers that initiate atrial fibrillation.
It is another objective of the present invention to enable the application of analyzing atrial arrhythmias, when atrial depolarization is obscured by the preceding ventricular repolarization.
It is another objective of the present invention to provide a tool that is used to develop and apply a database for classification of atrial arrhythmias.
The advantage of the present invention over the prior art is that it provides for a QRST subtraction algorithm based on using an adaptive QRST template while retaining the intricate spatial and temporal detail in atrial activity morphology, including P waves, fibrillation waves and flutter waves.
The present invention provides an apparatus and method for localizing and classifying atrial arrhythmias. More specifically, the present invention provides a noninvasive apparatus and method for analysis of TU wave obscured atrial activity. The present invention includes an apparatus and method to isolate atrial activity wherein atrial activity is commonly known as, but not limited to: (1) a P wave in case of focal atrial fibrillation, atrial tachycardia, and orthodromic AV reentrant tachycardia; (2) a fibrillation wave in case of atrial fibrillation other than focal atrial fibrillation; and (3) a flutter wave in case of atrial flutter.
When localizing arrhythmia foci or the insertion site of an accessory pathway within an atrium, the atrial activity that is indicative of activity within the atrium, is often superimposed, either partially or completely, by the TU wave. Physiologically speaking, the atrial activity of interest may coincide with ventricular recovery of the preceding cardiac cycle. To accurately localize focal triggers of atrial fibrillation, atrial tachycardia, and accessory pathway insertion sites during orthodromic AV reentrant tachycardia, the present invention provides for a noninvasive arrhythmia localization and classification apparatus and method for effectively and optimally separating the atrial activity of interest from a superimposed preceding ventricular activity. More specifically, the present invention provides a QRST subtraction algorithm based on using an adaptive QRST template that enables discrete isolation of TU wave obscured ectopic atrial activity on the surface ECG while retaining the intricate spatial and temporal detail in atrial activity morphology.
Accordingly, the present invention provides a signal processor which is identified as the apparatus and method that performs the processing to generate a QRST template that is further adapted and ultimately used in QRST subtraction to output an isolated atrial activity, e.g. a P wave, a fibrillation wave, or a flutter wave. The signal processor receives the electrical heart signals indicative of a heart""s atrial and ventricular activity obtained from the thoracic surface of a subject. After the QRST template is effectively subtracted from each measured signal containing an atrial activity of interest, the morphology of the isolated P wave, fibrillation wave, or flutter wave can be analyzed. Analysis parameters, such as for instance peak of the wave, duration of the wave, or multi-lead integral or potential map of the wave can be compared with a database containing a variety of analysis parameters of previously acquired P waves, fibrillation waves or flutter waves. The comparison with the database may then conclude on a localization or classification of a particular arrhythmia using noninvasive techniques upon which ablative treatment or another therapy decision would then be possible.
The present invention includes electrical heart signals that are acquired during sinus rhythm or atrial overdrive pacing. These electrical heart signals are used for the QRST template construction. For P wave and flutter wave isolation, the electrical heart signals that are used for QRST template construction have to be different from the electrical heart signal that is under investigation, i.e. the signal that is recorded during a particular arrhythmia (e.g. focal atrial fibrillation, atrial tachycardia, orthodromic AV reentrant tachycardia, or atrial flutter). Therefore, for P wave and flutter wave analysis, a clear distinction is made between the electrical heart signals obtained during an arrhythmia, called arrhythmia signals, and the electrical heart signals obtained during sinus rhythm or atrial pacing, called template signals that are used to create the QRST template. It is the arrhythmia signal that is eventually exposed to subtraction of the QRST template, after the template is adapted, to isolate the atrial activity that is obscured from the preceding heartbeat""s ventricular activity. In case of fibrillation waves, the QRST template may also be designed from the electrical heart signal that is under investigation, i.e. the signal that is recorded during chronic atrial fibrillation.
The present invention includes sensors adapted to detect electrical heart signals. The sensors are distributed in an array across the thoracic skin of a subject. Generally, this employs a plurality of sensors distributed across the anterior and posterior skin surface of the torso of the subject, or to an alternative accessible body surface, for example via a transesophageal approach. However, the present invention enables the use of at least one sensor. Electrical heart signals from each sensor are preferably acquired simultaneously, amplified and converted into digital signals using an analog-to-digital converter. The present invention includes and is not limited to the transmission of electrical heart signals to the signal processor either by conventional electrical cables/wires or by wireless communication. Also the present invention is not limited to combinations of either conventional and wireless communication of the signals. This then enables remote detection, analysis, operation and treatment.
In accordance to exemplary embodiments, the signal processor receives at least two template signals that contain electrical heart signals obtained during sinus rhythm or atrial pacing for the construction of a QRST template. In addition, the signal processor receives an arrhythmia signal that contains electrical heart signals obtained during an actual arrhythmia and in which atrial activity is obscured by ventricular activity. In case of fibrillation wave isolation one may use both the signal obtained from an arrhythmia signal, i.e. atrial fibrillation other than focal atrial fibrillation, or the signal during sinus rhythm or pacing to develop the template. While in case of P wave or flutter wave isolation it is imperative to use a template based on sinus rhythm or pacing.
An adaptation of the QT interval of the QRST template can take place to correct for differences in heart rate with the arrhythmia signal. One or more fiducial points and windows are identified and annotated for both the QRST template to create a so called annotated QRST template as well as for the arrhythmia signal to create a so called annotated arrhythmia signal. Alignment of the one or more fiducial points and windows annotated in the annotated QRST template and the annotated arrhythmia signal then takes place. After the alignment of the annotated QRST template and annotated arrhythmia signal, the annotated QRST template is resampled and modulated to further compensate for remaining discrepancies in duration and/or voltage. This creates a resampled and modulated QRST template. The atrial activity contained in the arrhythmia signal is isolated by subtracting the resampled and modulated QRST template from the arrhythmia signal. It is important to realize that the QRST template is adaptive to optimize the subtraction by first aligning the QRST template and then resampling and modulating the QRST template. The reason is to account for an arrhythmia discrepancy in heart rate and voltage amplitude of the QRST template with the TU complex of the arrhythmia signal. The present invention includes a variety of techniques that can be used to modulate and resample the QRST template. Generally, this approach of modulation and resampling allows for the surface ECG measurements to retain their intricate spatial and temporal detail within the P wave, fibrillation wave, or flutter wave morphology. The signal processor is capable of unmasking and preserving subtle electrical heart signal details of relatively low-voltage atrial activity signals despite the obscuring superimposed relatively high-voltage QRST complex.
Also in accordance to exemplary embodiments, after the QRST template is effectively subtracted from each measured signal containing an atrial activity of interest, the morphology of the isolated P wave, fibrillation wave or flutter wave can be analyzed in terms of analysis parameters. Examples of analysis parameters are for instance the peak of the wave or the time interval between onset and offset of the wave, or one or more multi-lead integral maps or potential maps of the wave. In an illustrative example an integral map was computed of the isolated P wave. This integral map can be compared with a database of P wave integral maps that was created by for instance pacing. This comparison enables that a particular arrhythmia can be localized from an arrhythmia signal that was obtained by noninvasive techniques. A variety of analysis parameters can be calculated and exchanged with the database. The same type of computation, comparison, or classification can be performed for fibrillation waves and flutter waves with databases containing fibrillation and/or flutter wave analysis parameters.
Finally, the present invention also provides for the application of analyzing and classifying atrial arrhythmias, when atrial depolarization is obscured by the preceding heartbeat""s ventricular repolarization.